Rotating plasma device



March 2, 1965 J. G. GORMAN ETAL ROTATING PLASMA DEVICE 4 Sheets-Sheet 1Filed May 17, 1963 APERTURE LIMITER 29 INSIDE DIAMETER SOURCE CONTROLOHMIC HEATING INVENTORS.

JOSEPH G. GORMAN BY LEONARDUS H. RIETJENS March 2, 1965 J. G. G'ORMANETAL ROTATING PLASMA DEVICE 4 Sheets-Sheet 2 Filed May 17, 1963 a nu032353229 March 1965 J. G. GORMAN ETAL 3,171,788

ROTATING PLASMA DEVICE Filed May 17, 1963 4 Sheets-Sheet 3 I l I l l l on o 1 g 0 Q A (D o g o E 2 g 0 a) v 0 g n) m n v I ll O 0 g -8 m P l- Nm o 2 o E o LIJ o 8 o E J A O 6 o O k l o o 0 o 0 o o o o 0 O 0 o g 9 cow v m 99s 11' awu .LNEIINEINIdNOD INVENTORS.

BY JOSEPH G. GORMAN LEONARDUS H. RIETJENS ATTORNEY March 2, 1965 J.GORMAN ETAL ROTATING PLASMA DEVICE 42 Sheets-Sheet 4 Filed May 17, 19633 L M .m n. ill 5 5 \l 9\\2 V H a\ m M u -m a N m mo 90 5 E sG NH w m D.O S 0A I V PVG IIR Q 08k 353 m. 34 I l B U 5 0 w w m m w c m 0 6 mm D Ae R \I n mw (a III l 3 n 15 w. R WIN? Q Q Q 0 0 m w m 5 i=300p. sec

I5 RADIUS (mm) FIG. 5b

FIG. 6b

INVENTORS.

JOSEPH G. GORMAN BY LEONARDUS H.R|ETJENS United States Patent 3,171,7ssRG'EATENG PLASMA DEVHQE Joseph G. German, Mercer County, Ndh, andLeonardus H. Rietjens, .lutphaas, Netherlands, assignors to the UnitedStates of America as represented by the United States Atomic EnergyCommission Filed May 17, was, Ser. No. 281,375 s Claims. (cl. 1l7-5-1)This invention relates to high temperature plasmas and means for heatingand confining high temperature plasmas.

Since the advent of thermonuclear research and development it has beendesirable to heat and confine high temperature plasmas. One approach tothis problem has been the stellarator in which the plasma has beenheated and confined in an endless discharge tube by means of anexternally imposed magnetic field.

In the stellarator described in US. Patent 3,015,618, a plasma of ionsand electrons has been ohmically heated in a cylindrical column while anexternally imposed axial magnetic confining field with a rotationaltransform has confined the heated plasma inside the discharge tube Witha substantially uniform density gradient across the heated plasmadiameter and substantially without rotation of the heated plasma as awhole around the tube. Also, the heated plasma has been neutrallycharged throughout its cross-section and there has been a substantiallyuniform diffusion coetficient across the heated plasma.

It has now been discovered that by properly positioning an exposedelectrical conductor deeply into the heated plasma, impressing a largepositive potential on this conductor relative to the discharge tube, andby drawing a large electron current through this conductor to disturbthe charge neutrality of a particular portion of the heated plasma, aninternally imposed, strong, annular radial electric field region isestablished in the whole outer region of the heated plasma which isreacted with the externally imposed axial magnetic confining fieldrapidly to rotate the heated plasma portion in the electric fieldregion, thus greatly to decrease the loss rate of the heated plasma tothe discharge tube wall.

Various other advantages will appear from the following description ofone embodiment of this invention, and the novel features will beparticularly pointed out hereinafter in connection with the appendedclaims.

In the drawings, where like parts are numbered alike:

FIG. 1 is a partial isometric View of a high temperature stellaratorhaving an endless discharge tube, external magnetic means, and means forpositioning the electric field producing conductor of this invention inthe stellarator tube;

FIG. 2 is a partial cross-section of the discharge tube of FIG. 1showing the intersection of magnetic surfaces and the electric fieldproducing conductor of this invention;

FIG. 3 is a partial cross-section of the electric field producingconductor of this invention and the means for positioning it in theendless discharge tube of FIG. 1;

FIG. 4 is a graphic representation of the confinement time of a heatedplasma in the stellarator of FIG. 1 as a function of the voltage on theelectric field producing conductor of this invention;

FIG. 5a is a graphic representation of the space poten tial vs. radiusin the stellarator tube of FIG. 1 without an electric field imposedtherein by the electric field producing conductor of this invention;

FIG. 5b is a graphic representation of the density profile vs. radius ofa heated plasma in the stellarator tube of FIG. 1 without an electricfield imposed therein by the electric field producing conductor of thisinvention;

FIG. 6a is a graphic representation of the space potential vs. radius inthe stellarator tube of FIG. 1 with an electric field produced thereinwith the electric field producing conductor of this invention;

FIG. 6b is a graphic representation of the density profile vs. radius ofa heated plasma in the stellarator tube of FIG. 1 with an electric fieldproduced therein with the electric field producing conductor of thisinvention.

Referring now to FIG. 1, non-magnetic, bakeable, endless discharge tube11 is stainless steel, except for ceramic portion 13, and forms anendless reaction chamber 15 inside the tube. A radial tubular duct suchas duct 17, serves as an inlet into the chamber 15 for reactive gas froma suitable source (not shown), and for evacuation of chamber 15 to ahigh vacuum, e.g., 10-- millimeters of mercury from a suitable source(not shown).

Advantageously, means such as an annular ferrite ring 19, disposedaround tube 11, has an electrical winding 21 and a radio-frequency highelectrical energy source (not shown) and operates to ionize gaseousatoms introduced into chamber 15. This produces a substantiallyneutrally charged plasma of ions and electrons in chamber 15. A suitableneutral plasma may, however, be injected directly into the chamber 15through a suitable duct like duct 17.

Laminated iron annular ring 23, also disposed around tube H, hassuitable windings 25 and a suitable audio frequency, high electricalenergy source (not shown), and operates ohmically to heat a centralcylindrical column 27 or ring of plasma all around tube 11. Annularfixed aperture limiter 29, which, for example, has an aperture diameterof 40 mm. co-axial with a 50 mm. inside diameter of tube 11, reduces thesize of the ohmic discharge to a cylindrical shape co-axial with theaxis 31 of tube 11 and to a thickness corresponding with the insidediameter of the limiter 29. The diameter of the plasma column 27 in FIG.1 across the center of tube 11, thus corresponds with the insidediameter of the aperture limiter 29.

Ion cyclotron resonance heating section 33 optionally may beadditionally disposed around tube 11 to provide additional plasmaheating by transferring energy to the plasma, e.g., by ion cyclotronheating. This energy may be thermalized by magnetic damping and to thisend suitable axial windings are arranged to provide a magnetic fieldgradient.

Divertor 41, located in one of the straight sections 43 of tube 11removes impurity ions from chamber 15 and to this end a suitable source(not shown) energizes suitable windings in the divertor to provide alocal magnetic field in reaction chamber 15 which locally distorts themain axially confining magnetic field lines 45, described in more detailhereinafter. This causes the axial confining field lines near the wallof tube ill to be bent into a chamber provided in the divertor and theyare bent through parallel, non-magnetic metallic impurity-ion-collectorplates in the divertor 4i. Advantageously tube 11 also carries externalheating elements (not shown) which bake tube 11 to high temperatures inexcess of 400 C. for long periods of time to help remove impurity ionsfrom tube ll through the above-mentioned vacuum system for tube ll.

On its outside circumference, tube 11 has external axial magnetic fieldwindings 51 all the way around tube 11, partially shown for ease ofexplanation, and associated external, oppositely, adjacently energized,helical windings 53 on both of the opposite end loops 57 of tube 11.Windings 5i and 53 advantageously both have the same electrical energysource, such as a high power direct current source (not shown) and thissource operates with these windings 51 and 53 to establish a highstrength axial magnetic field with a rotational transform around theaxis 31 of tube 11 in chamber 15. This high strength magnetic field,which may vary for various stellarator tube diameter sizes, for example,from a 38 kG field to a magnetic field of over 50 kG provideslongitudinally extending magnetic lines of force 45 which form manycylindrical magnetic surfaces 59 co-axial with the axis 31 of tube 11,as illustrated for ease of explanation in FIG. 2 by only two surfaces 59and 5%. Annular aperture limiter 29 has a hole diameter larger than thediameter of magnetic surface 59' (FIG. 2) which is described in moredetail hereinafter.

The mentioned magnetic surfaces 59 produce an inward magnetic pressuregreater than the outward plasma pressure and confine the plasma byimpeding the outward movement of the plasma particles across thesemagnetic surfaces 59 to the inside wall of tube 11. Heretofore, thedensity gradient of the neutral plasma in tube 11 has been substantiallyuniform from the tube axis 31 to the inside of the tube 11. With atungsten, flat, solid ring shaped, aperture limiter 29 inside tube 11,this density has been substantially uniform from the tube axis 31 toabout 5 mm. from the inside wall in a mm. radius tube 11 with anaperture limiter having a radius of 20 mm., as shown in FIG. 5b. Asshown in FIG. 5a there has also been a very small, substantially uniformor flat space potential from the tube axis 31 to the inside diameter ofthe aperture limiter 29.

In accordance with this invention electrical conductor 61, having alarge longitudinally extending, exposed area, is properly positioned bybiasing it into heated plasma column 27, transversely of the axialmagnetic field lines in tube 11 and so as to intersect the conductor 61with two or more magnetic surfaces such as inner and outer surfaces 59and 59 as shown in FIG. 2. Advantageously, the biasing of conductor 61is normal to the tube axis 31 in the plane of tube 11 in which straightsections 43 and end loops 57 are formed, but since the intersectingmagnetic surfaces are cylindrical, the biasing may be at other anglesthan normally to the axis 31. Also this biasing may be in a planeintersecting the plane of the tube 11 and its end loops 57 at an angle.Source 63 impresses a large positive potential on conductor 61 fromoutside tube 11 and conductor 61 intersects at least two spaced magneticsurfaces such as magnetic surfaces 59 and 59' that instantaneouslyconvey a large electron current flow to the conductor 61 from all aroundthe tube 11. The conductor 61 draws a large electron current from theplasma in column 27 greatly to disturb the charge neutrality of thisplasma all the way around tube 11 and produces an annular electric fieldregion 65 in the whole outer region of the heated plasma column 27 fromthe free end 62 of conductor 61 outwardly. This internally imposedelectric field interacts with the externally imposed axial magneticfield to rotate the portion of the plasma in heated plasma column 27which contains this electric field region 65 whereby the confinementtime of the plasma in heated column 27 is increased.

This confinement time is increased considerably as shown in FIG. 4, andsince the plasma temperature increase will correspond to the confinementtime increase, the plasma temperature also will be increased thus toincrease the value of the plasma as a research tool. Also, thisinvention decreases the plasma diffusion coefiicient without decreasingthe thickness of the heated plasma column 29. Additionally, whenincreasing the temperature sufficiently, increased numbers of usefulreaction products such as increased numbers of neutrons will beproduced.

In order to understand the operation of this invention in a highstrength magnetic field, reference is made to FIGS. 1 and 2. With apotential of several hundred volts positive on the conductor 61 withrespect to the wall of discharge tube 11, a large electron current isdrawn from the plasma. Then, because, a certain region of the plasma isstarved of electrons, the electric potential of this region rises. Thecharge neutrality of the plasma is thus purposely disturbed by drawing alarge electron current from only one position on a magnetic shellextending between two magnetic surfaces 59 in chamber 15, and thisraises the electric potential of the entire shell, all around the tube11, and establishes a radial electric field in the whole outer region 65of the cylindrical heated plasma in tube 11. This radial electric fieldacting with the axial magnetic confining field then causes the plasma torotate with a vector velocity given by EXB V=- where E the vector radialelectric field strength and i the vector axial magnetic field strength.It is this rotation of the plasma in electric field region 65 of column27, much faster than the loss rate of the plasma, which it is believedis responsible for decreasing the plasma loss rate by at least a factorof eight. Also, the plasma diffusing outwardly from the inner electricfield free region of column 27 in tube 1.1, rapidly is rotated uponentering the electric field region 65 so as to delay its travel to thewall of tube 11.

In a practical arrangement for the apparatus of this invention referenceis made to FIG. 3 which shows a 0.4 mm. diameter tungsten wire conductor61 extending to about 3 mm. beyond the end of a 1.3 mm. outside diameteralumina tube 67. The ohmic transformer heating is induced parallel tothe magnetic confining field by means of direct current source having a400 kw. or higher power amplifier and the plasma loop voltage isprogrammed with control 69 to obtain a discharge of approximatelyconstant conductivity. During this phase, which may last about 500 sec.or longer, the measurements illustrated in FIGS. 4, 5a, 5b, 6a and 6bwere made.

Advantageously conductor 61 has around its annular insulator 67 asuitable metal support '71. Also it has a suitable vacuum tight means 73for biasing the conductor 61 and suitably positioning it in the plasmain tube 11 at an angle to the tube axis 31. As shown in FIG. 3, thisvacuum tight biasing and positioning means 73 comprises a duct 75connected to tube 11 on the plane of the tube 11 and its end loops 57.This duct '75 has a flange '77, end plate closure 78 therefor and anannular array of bolts 79 for holding this closure in vacuum tightrelation with flange '77. Closure '73 also connects and supports, invacuum tight relation therewith, one end 81 of bellows 83. At the otherend 85, bellows 83 has a vacuum face seal assembly 87 and the conductor61, its insulator 6'7 and support '71 pass through the center of thisface seal assembly 87 and glass cap 38 with glass- Kovar-metal seal )0,which are in vacuum tight relation to maintain the vacuum inside thebellows 83 that communicates with the vacuum in chamber 15. Conductor 61passes through its insulator 67 the open end of its metal support 71,and a glass-tungsten press-seal in cap 83 therefor and past a metal yoke89 without touching the yoke to positive potential source 63 while theconductor is electrically insulated from tube 11.

Flange 77 also carries a longitudinally extending metal support 93 thatis slideably engageable with seal assembly 37 at end of bellows 83. Tothis end triangular metal bridge 95 connects with seal assembly 87 andthis triangular piece 95 passes through a suitable longitudinallyextending slot in support 93. Also, this triangular piece 95 carries asole plate 97 that normally holds the seal assembly from being liftedotf the top of support 93.

Support 93 also carries a rotatable sleeve 99 having a threaded aperture101 through which rod 103 threads for the inward and outward movement ofseal assembly 8'7. Atmospheric pressure acting on the face seal assembly87 creates a force inward toward tube 11 that is transmitted by way ofyoke 8h to rod 103 and hence through aperture Hi1 to sleeve 99 such thatsleeve 99 is held in contact with the right angle extension plate 104 ofsupport 93. By rotating sleeve 99 to move rod 103 inwardly toward tube11, stationary rod 103 thrusts yoke 89 and seal assembly 87 inwardlyalong the top of support 93 and in line with the slot therein throughwhich triangular bridge 95 passes. This biases conductor 61 inwardly. Byreversing the rotation of sleeve 99 the rod 103 draws yoke 89 and itsconnection with seal assembly 87 outwardly, oppositely from tube 11 andthis draws conductor 61 as well as its surrounding insulator 67 andsupport '71 outwardly from axis 31 in tube 11 in a line substantiallynormally to this axis 31 and in the plane of the tube 11 and its endloops 57.

Rod 103 also carries an inductor arm 105 that moves with rod 103 inrelation to index 107 on stationary support 93. distance of conductor 61from the center of tube 11 and thus the location of conductor er inchamber 15. Advantageously, a 0.4 mm. diameter conductor 61 with 3 mm.of the conductor 61 exposed beyond the end of its insulator 67 ispositioned with the tip 62' of the conductor 61 10 mm. from the axis 31of tube 11 in the heated plasma column 27.

With an exposed conductor 61 three mm. long at a radial position of 10mm. and +200 v. the conductor 61 draws all the electron current that candiffuse into the magnetic surfaces 59 and 50" intercepted by the exposedtip 62 of conductor 61 without damage to conductor 61. Under theseconditions the free charge distribution is shown in FIG. 611 by thedashed line 111 and the plasma density gradient is shown in FIG. 61;. Asshown, the space potential of the plasma is uniform from the center ofthe discharge to the radius of the inducing probe and has a value undermost conditions equal to or somewhat less than the potential ofconductor 61. From the radius of conductor end 62 to the radius of thecurrent channel 27, a more or less uniform electric field existsazimuthally symmetric about the magnetic axis 31 of the steliarator. Thespace potential at the edge of column 27 is approximately equal to 3.5times the electron temperature measured in ev.

If, instead of operating this large collecting area conductor 61 atconstant potential, a positive step voltage is impressed thereon, theconductor 61 current can be integrated to find the total charge neededto establish a given space potential V in stellarator tube 11. In thisway it is suggested that the conductor 61 of this invention establishesa plasma capacitor having a magnetic surface 59 as the inner plate, thedischarge tube 11 as the outer plate and the plasma therebetween as adielectric with a dielectric constant Also, it has been found that themeasured value of the radial electric field established by the conductorof this invention in a strong axial confining field, corresponds to aplasma rotation frequency of about 100 kc.

With regard to the diffusion of the plasma, the conductor 61 of thisinvention produces two regions in column 27 in which there are twodifferent difiusion coefficients. In the inner region 112 of column 27,Where there is substantially no radial electric field, the diffusion isrepresented by D In the annular outer electric field region 65 of column27, which surrounds the inner region 112 and where there is an averageradial electric field of about 200 v./cm., the diffusion is representedby D Although these diffusion coefficients are independent of plasmadensity, there is only a small density gradient observed in the innerregion 112 and a much larger density gradient in the outer region 65.Also, these two density gradients are produced without decreasing thewidth of the heated plasma column 27.

The best fit to the experimental points is obtained for D /D =8 and thisratio holds when moving the current drawing conductor 61 inwardly.Moving the conductor This index is scaled suitably to indicate the 7 end62 into an inner magnetic surface (not shown), e.g., to a radialposition of 8 mm. enlarges the outer region in Which the radial electricfieldand a larger density gradient exists thus variably and adjustablyto change the thickness of the inner and outer region 112 and whilemaintaining the same large diameter of heated plasma column 27.

In FIG. 4 the plasma confinement time T is plotted as a function of thevoltage on a 3 mm. conductor whose end 62 is located at a radialposition of 12 mm. with a constant conductivity plasma; the confinementtime is lengthened by a factor of 13 or longer from that knownheretofore, as the voltage on the conductor is raised to about 200 v.positive. In contrast to the constant diffusion of the plasma knownheretofore where the diffusion coefficient has been 2.1 10 cm. /sec. ormore for a 4 ev. plasma in a 38 kG field the diffusion coefficient inthe outer region with this invention, actually has been reduced to 1.3 X10 cm. /sec. or less. Also in contrast to the rather flat densityprofile when no radial electric field is applied, the density increasesfrom the tube wall to the interior of the plasma in the presence of theapplied radial field.

If the potential of the inducing conductor 61 is varied and the currentto this conductor i is ploted as a function of the space potential ofthe plasma at the radius of the inducing conductor V we find Plasmaconditions (fully ionized hydrogen plasma):

Electron density, 10 /cm. Electron temperature (conductivity), 4 ev.5ev. Plasma diameter, 50 mm. 1 Magnetic field, 38 kilogauss Rotation inelectric field region 65 about 100,000

revolutions/sec.

Conductor dimensions (tungsten wire):

Diameter, 0.4 mm.

exposed portion in plasma, 3 mm.

Ceramic tube, 1.3 mm. diameter Conductor end, 10 mm. from center ofplasma discharge Conductor potential, +200 v. with respect to dischargetube 11 Conductor current, about 0.6 amp.

Radial electric field 65: Cylindrical symmetry with respect to theplasma axis annular all around tube 11 between radial position 13 mm.and 25 mm. from axis 31 of tube 11.

Plasma loss: 1.3 10 cm. /sec. (for 4 ev. plasma) In the region 65 havingan imposed radial electric field the diffusion coefiicient is 13x10 cm./sec. for 4 ev. plasma. This is at least 8 times less than the loss ratein region 112 having no imposed radial electric field.

Reduced loss rate persists typically for duration of discharge which isup to 1 millisecond or more.

In other tests the high conductor potential of at least +200 v. wasapplied with plasma densities up to 3 X10 temperatures up to 25 ev., andmagnetic fields up to 40 kG Without any damage to the conductor 61 andwithout any significant change in the conductivity of the plasma at anypoint across the diameter of plasma column 2'7. In all these tests, theprobe was capable of collecting more electrons than could be suppliedreadily by the plasma and to this end the current of conductor 61 wasmaintained close to the saturation electron current. Thus,

assuming that the electrons were supplied from the shell defined by themagnetic surfaces intercepted by the exposed conductor 61, then the flowof electrons into this shell was less than the saturation electroncurrent.

In order to set an analytical expression for this latter inequality,assumptions are made about the type of diffusion taking place and thedensity gradients existing in the plasma. A rough model, assumingpumpout is a diffusion process that goes as T /B, leads to theexpression 1 2 gi const. where T, is the electron temperature, B is themagnetic field, r is the radius of the conductor end, and a is thecollecting area of the probe. Observations so far fit this modelqualitatively.

Actual tests have also shown that the conductor of this inventionprovides confinement time that increases with the square of the magneticconfining field and also increases with the electron temperature. Thisis entirely difierent from the confinement shown in stellaratorsheretofore.

The conductor of this invention and the electric field produced therebymakes the ohmically heated stellarator a more useful device for plasmaphysics experiments and at sufficiently high temperatures for increasedreaction products therefrom. Also, the heretofore known high pump-outdiffusion has, at least in part, been nullified by this invention. Theconfinement time has been shown to be increased at least two-fold withthis invention and with increased magnetic confining fields andincreased stellarator sizes this increase in confinement will be evengreater. This invention also will provide plasma confinement such as isnecessary in realizing an economical thermonuclear reactor and to thisend this invention may be used for igniting the plasma in a full scalecontrolled thermonuclear reactor.

What is claimed is:

1. In a method for increasing the confinement time of a high temperatureplasma in a stellarator having confining coils which produce an axialmagnetic field including axial field lines forming cylindrical magneticsurfaces for magnetically confining the plasma, an evacuated metallicendless tube inside said coils, means for providing in said tube acylindrical neutrally charged plasma of ions and electrons, and meansfor ohmically heating to high temperature a column of said plasma whichsaid magnetic field confines in said tube along the axis of said tubewhile said hot plasma column is being heated to a high temperature, theimprovement comprising withdrawing large numbers of electrons in adirect flow from said plasma in said tube through a thick positivelycharged conductor having a free exposed end, said end being within saidcolumn thereby to disturb the space charge neutrality of said plasmasufiiciently to establish an annular radial electric field region fromsaid free end of said conductor outwardly, said electric fieldinteracting with said axial magnetic field produced by said coils tocause said plasma in said electric field region to rotate rapidly aroundsaid stellarator thereby to increase the confinement time of said plasmain said high temperature column of said plasma, and moving saidconductor for controlling said electric field region thickness.

2. A method for increasing the confinement time of a high temperatureplasma in a stellarator having confining coils which produce an axialmagnetic field including axial field lines forming cylindrical magneticsurfaces for magnetically confining the plasma, an evacuated metallicendless tube inside said coils, means for providing in said tube acylindrical neutrally charged plasma of ions and electrons, and meansfor ohmically heating to high temperature a column of said plasma whichsaid magnetic field confines in said tube along the axis of said tubewhile said plasma column is being heated to high temperature,

comprising withdrawing large numbers of electrons in a direct flow fromsaid plasma in said tube through a single, thick, exposed, positivelycharged, free, conductor end positioned within said plasma to disturbthe charge neutrality of said plasma sutficiently to establish anendless, annular, radial electric field region from said free conductorend outwardly which interacts with said axial magnetic field produced bysaid coils to cause said plasma in said electric field region to rotaterapidly around said stellarator thereby to increase the confinement timeand temperature of said plasma in said high temperature column ofplasma, and moving said conductor in a direction to increase thethickness of said electric field region.

3. The invention of claim 1 in which said exposed free conductor end isabout half way into said plasma column and produces an inner firstplasma diifusion zone, column half way across said plasma column and anouter annular cylindrical second plasma diffusion zone across theremaining half of said plasma column, said plasma diffusion being sloweracross said second zone than across said first zone toward said tubeWall, and wherein said conductor is moved away from the center of saidhot plasma column to remove said conductor away from said hot plasmacolumn.

4. In a stellarator having confining coils which produce an axialmagnetic field for magnetically confining a high temperature plasma, anevacuated metallic endless tube inside said coils, and means forproviding in said tube a cylindrical column of hot ionized plasma whichsaid coils confine in said tube along the axis of said tube, a rotatingplasma means, comprising a positive source of potential having a highvalue relative to said tube, a conductor in said plasma column having anexposed conductor end and means for insulating said conductor from saidtube, means for biasing said conductor at an angle to the tube axis toconnect said plasma to said source of potential from only one positionin said plasma, said conductor being so positive as to deplete saidplasma of electrons adjacent said conductor with a current flow in saidconductor sufiicient to draw electrons from all around the stellarator,said flow of electrons establishing an annular cylindrical radialelectric field in hot ionized plasma from said conductor end to theoutside of said plasma column, said electric field being in operableassociation with said magnetic field produced by said coils for causingsaid electron depleted lasma to rotate rapidly around said stellaratorthereby to increase the confinement time and temperature of the plasmain said hot ionized column.

5. In a stellarator having confining coils which produce an axialmagnetic field having axial field lines forming cylindrical magneticsurfaces for confining a high temperature plasma, an evacuated metalendless tube inside said coils, an annular aperture limiter, and meansfor providing a column of hot ionized plasma inside said aperturelimiter which said coils confine in said tube along the axis of saidtube, a rotating plasma means, comprising a positive source of potentialwhich is high in value relative to said tube, a conductor having anexposed end extending longitudinally into said tube at an angle to saidtube axis so as to intercept several of said magnetic surfaces, meansfor selectively biasing said conductor end into said column of hotionized plasma, said conductor end having a large cross-sectional areafor drawing all the electron current that can diffuse into said magneticsurfaces intercepted by said exposed conductor end, said conductordrawing all this electron current from said plasma to produce an annularpositive, radial, space potential relative to said tube from the exposedconductor end to the inside diameter of said tube along the axis of saidtube and a corresponding annular electric field, said electric field andmagnetic field being in operable association rapidly to rotate saidplasma around the axis of said tube whereby the confinement time andtemperature of said plasma are increased.

6. In a stellarator having confining coils which produce an axialmagnetic field of at least 38 kilogauss for magnetically confining ahigh temperature plasma, an evacuated metal endless tube inside saidcoils, means for providing in said tube a cylindrical plasma having anelectron density of at least l /cm. an electron temperature conductivityof 5 ev., a plasma diameter of at least 50 mm, and means for providing acolumn of hot ionized plasma which said coils confine in said tube alongthe axis of said tube, a rotating plasma means, comprising a positivesource of potential having a 200 v. positive potential relative to saidtube, a conductor having an exposed end extending transversely into saidtube at an angle to the axis of said tube, means for selectively biasingsaid conductor end to about mm. from the center of said column of hotionized plasma, said end of said conductor having a cross-sectionaldiameter of about 0.4 mm., and removing large numbers of electrons fromsaid plasma at a current of about 0.6 ampere, said conductor currentproducing a positive radial plasma space potential relative to said tubefrom said exposed conductor end to the outside of said column of hotionized plasma and a corresponding radial electric field region having acylindrical symmetry with respect to the axis of said tube all aroundsaid stellarator, said electric field being in operable association withsaid magnetic field produced by said coils rapidly to rotate said plasmain said electric field region around the stellarator at a speed of about100,000 revolutions per second whereby the confinement time andtemperature of the plasma column is increased.

7. Means for producing an annular rotating plasma of variably adjustablethickness, comprising means for producing an ohmically heated column ofhot ionized plasma, an endless evacuated metal shell surrounding saidplasma and having coils supported on the outside of said shell forproducing an axial magnetic plasma confining field with a rotationaltransform inside said shell, an exposed conductor end having means formaintaining said conductor end positively charged with respect to saidmetal shell, and means for variably adjustably biasing said conductorend transversely to said magnetic field and positioning it deeply intosaid column of hot ionized plasma so that there is a direct flow ofelectrons to said conductor from said plasma that produces an outerannular electric field in said plasma column around the length of themetal shell, said electric field operating with said magnetic fieldrapidly to rotate the plasma in said electric field, the thickness ofsaid rotating plasma corresponding to the depth to which said conductorend is positioned into said column of hot ionized plasma.

8. Means for producing an annular rotating plasma of variably adjustablethickness, comprising means for producing an ohrnically heated column ofhot ionized plasma, an endless evacuated metal shell surrounding saidplasma and having coils supported on the outside of said shell forproducing an axial magnetic plasma confining field with a rotationaltransform inside said shell, an exposed conductor end having means formaintaining a high positive potential on said exposed conductor end withrespect to said metal shell, means for variably adjustably biasing saidexposed conductor end transversely to said axial magnetic field so as toposition it deeply into said column of hot ionized plasma whereby saidmagnetic field rapidly transports plasma electrons to said conductorfrom around the length of said metal shell and produces an outer annularelectric field region around an inner electric field free region in saidcolumn of hot ionized plasma, said plasma in said electric field regioninteracting with said axial magnetic field rapidly to rotate the plasmain said annular electric field region, and means for indicating theposition of said exposed conductor end with respect to the center ofsaid column of hot ionized plasma whereby the thickness of said rotatingplasma is selectively adjustable with respect to said exposed conductorend.

References Cited by the Examiner UNITED STATES PATENTS 3,088,894 5/63Koenig 176l FOREIGN PATENTS 839,247 6/60 Great Britain.

CARL D. QUARFORTH, Primary Examiner.

REUBEN EPSTEIN, Examiner.

1. IN A METHOD FOR INCREASING THE CONFINEMENT OF A HIGH TEMPERATUREPLASMA IN A STELLARATOR HAVING CONFINING COILS WHICH PRODUCE AN AXIALMAGNETIC FIELD INCLUDING AXIAL FIELD LINES FORMING CYLINDRICAL MAGNETICSURFACES FOR MAGNETICALLY CONFINING THE PLASMA, AN EVACUATED METALLICENDLESS TUBE INSIDE SAID COILS, MEANS FOR PROVIDING IN SAID TUBE ACYLINDRICAL NEUTRALLY CHARGED PLASMA OF IONS AND ELECTRONS, AND MEANSFOR OHMICALLY HEATING TO HIGH TEMPERATURE A COLUMN OF SAID PLASMA WHICHSAID MAGNETIC FIELD CONFINES IN SAID TUBE ALONG THE AXIS OF SAID TUBEWHILE SAID HOT PLASMA COLUMN IS BEING HEATED TO A HIGH TEMPERATURE, THEIMPROVEMENT COMPRISING WITHDRAWING LARGE NUMBERS OF ELECTRONS IN ADIRECT FLOW FROM SAID PLASMA IN SAID TUBE THROUGH A THICK POSITIVELYCHARGED CONDUCTOR HAVING A FREE EXPOSED END, SAID END BEING WITHIN SAIDCOLUMN THEREBY TO DISTURB THE SPACE CHARGE NEUTRALITY OF SAID PLASMASUFFICIENTLY TO ESTABLISH AN ANNULAR RADIAL ELECTRIC FIELD REGION FROMSAID FREE END OF SAID CONDUCTOR OUTWARDLY, SAID ELECTRIC FIELDINTERACTING WITH SAID AXIAL MAGNETIC FIELD PRODUCED BY SAID COILS TOCAUSE SAID PLASMA IN SAID ELECTRIC FIELD REGION TO ROTATE RAPIDLY AROUNDSAID STELLARATOR THEREBY TO INCREASE THE CONFINEMENT TIME OF SAID PLASMAIN SAID HIGH TEMPERATURE COLUMN OF SAID PLASMA, AND MOVING SAIDCONDUCTOR FOR CONTROLLING SAID ELECTRIC FIELD REGION THICKNESS.